1. Field of the Invention
The present invention relates to a roller conveyor for conveying elongated articles such as skids used, for example, in an automobile painting line.
2. Description of the Related Art
Conventionally, in an equipment or line for painting the bodies of automobiles, in order to prevent mutual collision between the adjacent automobile bodies during conveyance, each automobile body to be painted is placed on a skid having a length larger than the length of the automobile body. The automobile body carried on the skid is then conveyed by a roller conveyor A1 such as shown in FIG. 7.
The roller conveyor A1 includes an elongated rectangular conveyor frame A2 disposed on a floor surface, a number of flanged free rollers A3 disposed on and along one longitudinal edge of the conveyor frame A2, and a number of drive rollers A4 disposed on and along the other longitudinal edge of the conveyor frame A2 at respective positions corresponding to the positions of the flanged free rollers A3.
Each of the flanged free rollers A3 is freely rotatable about a horizontal axis and has a pair of annular flanges F, F at opposite ends of an outer peripheral surfaces thereof. The annular flanges F, F serve to guide opposite side surfaces of an roller engagement portion t which is provided at the bottom of one skid leg A6 of a skid A5 on which a work W is carried. The outer peripheral surface of the flanged free roller A3 supports an undersurface of the roller engagement portion t of the skid A5.
Each of the drive rollers A4 has an outer peripheral surface on which the undersurface of a roller engagement portion t of the other skid leg A6 of the same skid A5 is supported. The drive roller A4 is driven in rotation by the built-in drive motor, so that the skid A5 is conveyed on the roller conveyor A1.
The skid to be conveyed by the roller conveyor is preferably constructed as light as possible so as to improve the conveyance efficiency and the thermal efficiency during conveyance through a drying furnace with a painted automobile body carried on the skid. Additionally, the skid generally has an elongated structure having a length of 5 to 6 meters and a width of about 800 millimeters. Accordingly, the skid of the foregoing construction is likely to be distorted when subjected to a load during conveyance or manufacture thereof.
Due to the distortion of the skid, the roller engagement portion on the skid leg of the skid being conveyed on the roller conveyor may disengage from the outer peripheral surface of the drive roller. Thus, the drive roller fails to transmit a sufficient driving force to the skid, lowering the conveyance efficiency of the roller conveyor.
Particularly in the case of a roller conveyor including a succession of free rollers each disposed between two adjacent ones of the drive rollers, it may occurs that the roller engagement portion of the skid is in contact with one free roller alone while separating from the adjacent drive roller, thereby disenabling further conveyance of the skid.
To cope with this problem, at least one longitudinal edge of the conveyor frame which is adapted to face the corresponding skid leg must be equipped exclusively with the drive rollers. This arrangement, however, requires an increased number of drive rollers, makes the conveyor roller complicated in construction, and increases the manufacturing cost of the conveyor roller.